This invention relates to photodetector mounting assemblies. In particular, the present invention is an improved construction and process for construction of infrared detector mounting assemblies of the Dewar type.
Infrared photodetectors are operated at low temperatures in order to obtain improved detector performance. The detectors are typically mounted in a double flask of the Dewar type. A Dewar flask consists of an inner flask and an outer flask. The infrared detectors are mounted in thermal contact with the top surface of the inner flask, which is cryogenically cooled. The detectors, therefore, operate at the cryogenic temperature.
Since the Dewar typically maintains a vacuum environment around the detectors, electrical connection between the detectors in the evacuated portion of the Dewar and outside of the Dewar has been rather complex. Fabrication techniques used to mount the detectors in the Dewar and to provide electrical connection from the detectors to the outside of the Dewar typically have involved a large number of hand or manual fabrication steps. These manual fabrication steps are time-consuming, tedious, expensive, and generally unsatisfactory.
One particularly difficult problem has been the providing of vacuum tight feed-throughs from the evacuated portion of the Dewar to the outside or non-evacuated portion of the Dewar. The problem becomes particularly difficult when large numbers of detectors are mounted in the Dewar. For example, many present applications require more than 100 feed-throughs. Separate handling, holding, and fusing of feed-throughs on an individual basis becomes prohibitive.
In the past, some improved techniques for fabricating feed-throughs in a Dewar have been suggested, such as the method described in U.S. Pat. No. 3,719,990 by J. J. Long et al. In this method, vacuum feed-throughs are inserted through the side walls of the outer flask of the Dewar. The feed-throughs are in the form of a plurality of conductive strips which are mounted in spoke-like orientation on an outer supporting rim. A somewhat similar arrangement of feed-throughs is shown in U.S. Pat. No. 3,851,173 by C. O. Taylor et al.